1. Field of the Invention
The present invention relates to a golf club head and, more particularly, to score lines on the face.
2. Description of the Related Art
Generally, on the face of a golf club head, a plurality of straight grooves are formed parallel to each other in the toe-and-heel direction (see, e.g., Japanese Patent Laid-Open Nos. 10-248974 and 2005-169129). These grooves are called score lines, marking lines, face lines, or the like (to be referred to as score lines in this specification). These score lines have an effect of increasing the back spin amount of a shot or suppressing a significant decrease in the back spin amount of a shot in the case of a rainy day or a shot from rough.
As a rule about score lines of a golf club head for competitions, each edge of a score line must be positioned within a virtual circle with a radius of 0.011 inches concentric with a virtual circle with a radius of 0.010 inches which internally touches the side surface of the score line and the face (to be referred to as a two-circle rule, hereinafter).
In order to satisfy the two-circle rule, however, it is necessary to decrease the angle between each side surface of the score lines and the face. In this case, the edge angle of the score line increases, resulting in not only a decrease in spin amount but also a decrease in the volume of the score line. Accordingly, a spin amount may significantly decrease in case of a shot from rough or a shot in a rainy day.